Before we start analysing the lab data for changes of variability and extreme events as a function of the North-South temperature gradient, it is instructive to inspect some of these features in the National Centers for Environmental Prediction (NCEP) reanalysis data [1]}.
In contrast to operational counterparts, the reanalysis data do not suffer from inhomogeneities introduced by changes in the data assimilation system. In this respect, they are better suited for studying variability and climate trends than data based on individual instrumental records or climate-model simulations [2]}.
Moreover, reanalysis data cover historical data as well. We use two temperature data sets from the collection “NOAA-CIRES 20th Century Reanalysis, version 2, Daily Averages”, covering the period from 1871 to 2012. The first set is the daily ensemble mean pressure level data (1000hPa to 10hPa), from which we extracted just the 500hPa level. The second set is the daily ensemble mean tropopause data.
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